It is increasingly common for more and more information to be stored electronically, rather than, as in the past, on physical records. It is also increasingly common for such information to be stored in a distributed fashion rather than at a single, or small number of, central locations. For example, information concerning individual items of equipment, such as service histories, are increasingly being maintained electronically by means of local memory devices physically attached to the equipment. An example of a suitable memory device for this application is the “Memory Spot” developed by the current applicant, which includes an electronic memory, a data processor and communication means integrated onto a single silicon chip. The local electronic memory can be updated whenever an action is performed on the piece of equipment, such as the replacement of a part or the completion of a routine maintenance action.
The use of local electronic memory is also increasingly common in applications where the stored data is preferably either maintained or verified by an issuing authority. For example, in the previous example the replacement of a part for a particular piece of equipment may be required to maintain the manufacturer warranty conditions and its replacement must therefore be verified in some manner by the authority providing the warranty, such as the manufacturer, so that they can be confident that the warranty conditions have been met by the equipment owner or user. Where such records were previously maintained centrally the act of updating the record itself could be performed by the issuing authority. However, where the information is stored electronically locally, an alternative method of either updating or verifying the information must be found. A further example of this requirement is the update of certain officially issued personal documents, such as a driving licence, identity card or passport. Previously where such documents were issued as physical documents any change of information, such as a change of the owner's address details or the addition or deletion of information such as driving licence endorsements, required the return of the physical document to the issuing authority for updates or and subsequent issue of a new, updated, physical document. As progress is made to replace such documents with electronic versions, such as smart cards, it is desirable for the information held on such electronic documents to be updated by the issuing authority without the physical return of the electronic document to that authority, yet for the data update to be performed to the satisfaction of the issuing authority.
Generally speaking, the increased use of locally stored data also increases the danger of that data quickly going out of date or loosing its synchronisation with a corresponding data record held by a relevant authority.